Occasions arise wherein a circuit designer of an electronic circuit that includes a silicon strain gauge transmitter or sensor is required to compensate for variations in temperature that occur. In order to maintain the accuracy of the measurements within specified limits, it is known to generally use an independent, separate element or component to compensate the positive temperature coefficient of sensitivity(with constant current) of the silicon strain gauge pressure transmitter. For example, the curves for typical silicon strain gauge pressure transmitters (sensors) have a slightly positive temperature coefficient of sensitivity with constant current excitation. Under conventional practice the circuit would need or use an additional thermally sensitive resistor, also known as a thermistor, with a positive temperature coefficient of sensitivity to temperature to compensate for the effects of temperature. Thus the circuit is adjusted to compensate for the effects of temperature by reducing current slightly as temperature increases.
It is known in the art, shown in FIG. 1, that the output 1a of an operational amplifier 1 is connected to one node (input node) 2a of a strain gauge bridge 2 and another node (output node) 2b of the strain gauge bridge 2 is connected to an inverting input 1b of the operational amplifier 1. The output node 2b is also connected to one end of a current sampling resistance R.sub.c (which may be a thermistor). The other end of the current sampling resistance R.sub.c is connected to ground or a zero voltage point. A positive terminal of a reference voltage, V.sub.ref, represented by a voltage source, such as a battery, is connected to a non-inverting input 1c of the operational amplifier 1, with negative end of said battery connected to the zero potential point.
It is also known in the art that, in practice, thermistors are non-linear devices which tend to limit or compromise the measurement accuracy of the strain gauge. Additionally, a thermistor's parameters may shift value upon exposure to high temperature, which would compromise the measurement range. Prior to this invention, designers were limited to using a non-linear element, such as a thermistor, to compensate the current variations due to temperature change. Furthermore, the time constants of the strain gauge bridge and the thermistor may be different, resulting in the compensation lagging or leading the temperature induced change in bridge resistance. As can be appreciated, this technique does not provide an optimum solution for accurately compensating a silicon strain gauge based system within a temperature range, such as a pressure sensor.